A refractive index of a material is a number that describes how light energy is propagated through that material. The refractive index is dependent on the wavelength propagated through it such that the refractive index may be different for varying wavelengths in the same material. Many transparent materials have a refractive index between 1 and 2. For example, air has a refractive index of 1, and water has a refractive index of 1.333.
Light transmitting materials may be used in circuit devices to relay information. For example, a core made of a transparent material with an appropriate refractive index may carry modulated light signals. Generally, the core has a refractive index that is higher than the refractive index of the cladding. In some cases, the core is made of silicon with a refractive index of 3.51 and the cladding is made of silicon dioxide with a refractive index of 1.46. Due to the phenomenon of total internal reflection where light tends to stay within materials with the higher refractive index, the core material acts as a wave guide that transmits optical signals.